This battery behaviour ( BlueNova Energy MPS BN13V-8-104Wh ) do appear at times, depending on the specific application the battery is used in.
The charger circuits in these “ household “ applications ( electric fence energiser, gatemotor, alarmsystem, etc ) , like you would know, is designed primarily for SLA (Sealed Lead Acid ) battery types and charging conditions.
The SLA charge curve is “ usually “ + - 13.85V ( max ) in Float mode .
In our experience, also like you mentioned, in most applications as mentioned above, the MPS LiFePO4 works “ fine “ although the LiFePO4 charging curve differ ever so slightly from the SLA charging curves.
The “ big difference “ comes with the mentioned + - 13.85V or even lower.
The MPS LiFePO4 ( not only applicable to BlueNova Energy LiFePO4 battery models...) has the following charge curve –
“Bulk / Absorbtion“ Voltage - min. 14.10V - 14.20V ( most manufacturers indicate “ 14:40V “ ...)
“ Float “ Voltage - + - 13.85V ( not that critical...)
The MPS LiFePO4 battery’s internal BMS needs at least 14.10V during the charge cycle to be able to start balancing the cells.
Therefore, where a SLA charger, which max charge to 13.85V is used, cell balancing obviously does not happen which in turn will result in a max SOC ( State of Charge ) of + - 95% .
In our experience, even under such conditions, the MPS LiFePO4 battery way out performs it’s SLA rivals.
BUT.....in some cases, over time, the LiFePO4 battery can become unbalanced to the point that it cannot performs as “ expected “ and even like in this case, suffer from premature shutdown .
To “ fix “ this undercharged state in the MPS LiFePO4 battery unit, is fairly easy .
You need to get yourself a 12V 10A Switch Mode Power Supply unit, as per below sample picture & link, to give the MPS battery the necessary “ balance charge “ .
To do this, the MPS LiFePO4 battery needs to be removed / disconnected from the application .
The power supply must be setup to supply 14.20V by adjusting the small voltage adjustment “ pot “, indicated with the red arrow. ( please use necessary care when adjusting...be gentle when adjusting with a small star or flat screwdriver ...)
A multimeter should be used to confirm the DC output voltage on the power supply while adjusting the “ pot “ .( voltage must be adjusted before connected to the battery ...)
Once the power supply is connected to the battery and supplying voltage to the battery, please monitor the battery terminal voltage and confirmed once it is at 14.20V .
Once at this voltage, please leave the power supply connected ( still “ charging “ ) to the battery for another hour whereafter the power supply can be removed.
If you are familiar with using a multimeter, the multimeter can be connected inline on the positive battery / charger side, in current measurement mode, to confirm the charging current has tapered down to “ 0 A “ or closest to this value .
Now the MPS LiFePO4 is balanced charged and can be reconnected in the application.
To keep the MPS LiFePO4 battery “ in the best possible condition “, the power supply DC output can now be adjusted back to 14:00V and connected in parallel with the battery terminals inside the application.
The MPS LiFePO4 battery can stay connected to the power supply, set at 14:00V, “ indefinite “ .
I would strongly recommend to use an AC inline fuse ( 1A ) on the switch mode power supply AC230V input as a “ surge protection device “ and / or even a reputable “ plug-in “ surge protector unit for additional safety. ( we don’t want the charger getting a surge / spike , go faulty and overcharge / short circuit te MPS LiFePO4 battery unit )
https://www.takealot.com/dc-12v-10a-120w-power-supply-mrul/PLID90071037
https://www.takealot.com/surge-protector-plug-for-loadshedding/PLID92716967